Extend SheetImage sample with cropped sprites

I recreated the Texture Packer sprite sheet and set the "Trim mode"
to "Crop, flush position" instead of "Trim". In the sample you can
now see that the trimmed sprites have 64x64 pixel bounds, while the
cropped ones are smaller.

The cropped sprites are rendered as they are, while the trimmed ones
use a MOAIBoundsDeck (see cef53f81d677e1ab703b99222974ddeaa1a933a9).

This is a follow-up to pull request #41.